Purification of sulfolene



United States Patent Ofifice 3,077,479 Patented Feb. 12, 1963 3,077,479lPURlFiCATllQN F SULFULENE Daniel B. Listen, in, and Friedrich G.Heltferich, Berkeiey, Calif., assignors to Shell @il Company, New York,N.Y., a corporation of Delaware No Drawing. Filed May 5, 1961, er. No.107,932 9 (Iiaims. (Cl. 260--332.1)

This invention relates to the manufacture of sulfolane and homologuesthereof, particularly lower alkyl sulfolanes of up to about eight carbonatoms. More particularly, it relates to an improvement in the reactionof 1,3- diolefins with sulfur dioxide to form sulfolenes and thecatalytic hydrogenation of the sulfolenes to sulfolanes.

The sulfolanes are well known solvents useful .in extractivedistillations, solvent extractions, and the like, especially inpetroleum processing for the separation of hydrocarbon mixtures. Theyare prepared by reacting a coniugated diolefin with sulfur dioxide andhydrogenating the resulting sulfolene to the corresponding sulfolene.Thus, sulfolane and the monoand dimethyl sulfolanes are prepared byreacting butadiene, methylbutadiene (isoprene, trans-piperylene), anddimethylbutadienes With sulfur dioxide to form sulfolene, methylsulfolene, and dimethyl sulfolene, respectively, and then catalyticallyhydrogenating the particular sulfolene, as by using a Raney nickelcatalyst, to the corresponding sulfolane.

The crude reaction product from the reaction of the diolefin with sulfurdioxide, even after conventional removal of excess S0 and any insolublepolysulfones, is not readily hydrogenated with any practical degree ofefficiency due to short catalyst life. The exact nature of the catalystpoison(s) is not known. There seem to be various possibilities.Neutralization With caustic followed by separation from inorganicsulfite salt formed from excess sulfur dioxide, or simply stripping withan inert gas, have not solved the problem. Heretofore, the difficultyhas been reduced by fractional crystallization of the sulfolene from thereaction product in an attempt to provide a purer sulfolene for thehydrogenation. This technique, however, is not only time-consuming andrequires considerable capital expenditure for plant-scale operation, butit results in a substantial reduction in yield of sulfolane.

A well known method for producing the sulfolene comprises conducting thereaction between the conjugated alkadiene and sulfur dioxide in asolution of a monohydric alcohol having from 1 to 4 carbon atoms, suchas, for example, isopropanol. The product sulfolene is subsequentlyhydrogenated to form sulfolane usually in the presence of Raney nickelcatalyst. This type of catalyst, as has been considered hereinbefore, issuscpetible to poisoning by sulfur-containing materials, and especiallyby sulfur dioxide. Moreover, the diolefin plus sulfur dioxide reactionis reversible, and upon standing the sulfolene product reverts in partinto its constituents includ ing sulfur dioxide.

It is therefore a principal object of this inventon to provide improvedmeans for the treatment of the reaction products of butadiene andrelated conjugated diolefins, e.g., butadienes of 4 to 8 carbon atoms,with sulfur dioxide whereby a sulfolene is formed. It is a furtherobject to provide an improved and greatly refined sulfolene product forhydrogenation with a sulfur-sensitive catalytic material, as forexample, Raney nickel.

Another important object of the invention is to remove sulfur dioxidefrom sulfolene, thereby providing a feed of higher quality for furtherchemical processing. A still further object of the invention is toprovide an improved process for the synthesis of sulfolane. Otherobjects and features of advantage will be apparent from a considerationof the following description of the invention.

The condensation product of sulfur dioxide with butadiene is, as hasbeen set forth heretofore, sulfolene. It is preferred to carry out thisreaction so as to obtain 3- sulfolene isomer which is more readilyhydrogenated than Z-sulfolene. This material, after treatment todeactivate catalyst poisons, is then hydrogenated at about 30 C. overRaney nickel catalyst with a conversion of about 97%. In general, thishydrogenation should be carried out within about 12 hours, andpreferably within about 6 hours, following the purification treatment;substantially immediate hydrogenation is advantageous.

Sulfolene can also be produced by reacting sulfur dioxide and butadieneat about C. in an isopropanol solution. At 1:1 mole ratio of sulfurdioxide to butadiene the conversion to sulfolene of the butadiene isabout 60-65%. According to earlier procedures both unreacted sulfurdioxide and butadiene are removed by boiling at about 60 C. and 15p.s.i.a. Following this, the composition of the reactant mixture ispredominantly as indicated in Table I.

TABLE I Component: Percent wt. lsopropanol 66.5 Sulfur dioxide 3.0Polysu-lfone 0.5 sulfolene 30.0

From the foregoing Table I, it will be appreciated that 3% by weightsulfur dioxide still remains. Even if this existing sulfur dioxide werecompletely removed by stripping, decomposition of sulfolene duringstorage or extended handling will produce additional sulfur dioxide. itis important that sulfolene solution be stored in a slightly warmenvironment in view of its solubility limitations. The decompositionrate constant at 40 C. is 5X10 per minute. Calculations based on thisrate constant indicate that after one Weeks storage of 30% w. solutionof sulfolene at 40 C., the material will contain about 770 ppm. sulfurdioxide.

In accordance with the present invention the sulfur dioxide present inthe reaction products from the sulfolene synthesis in a solution ofalcohol is removed by means of anionic exchange with a strong base"anion exchanger resin in salt form. Sulfur dioxide can be removed fromthe sulfolene by an anion exchanger in OH form, but the OH" ionscatalyze the addition of alcohols (as well as any Water present) to thesulfolene double bond. It has, however, been found that the use of theanion exchanger in the CO form effectively removes the sulfur dioxidewithout adversely affecting the sulfolene. In accordance therewith, theprimary process for the sulfur dioxide removal is delineated by thefollowing equation:

(R+ 2SO3=+ S02 2R+S'O3H Over-all the reaction then can be representedas:

In view of the fact that the reversion of sulfolene on standing formsundesired S0 it is most advantageous to provide for the removal of thecontaminating S immediately prior to the catalytic hydrogenation step.

As a further important advantage of the invention the ion exchange bedcan be readily regenerated with aqueous Na CO In performing theregeneration, it is advantageous to drain the column and to effect theregeneration by upflow therethrough in view of the fact that the resinexpands when it is brought into contact with an aqueous solution.Moreover, if water is particularly objectionable in the product, it canbe removed from the column following regeneration by washing brieflywith an alcohol such as methanol or isopropyl alcohol. A liberal excessof Na CO may be found desirable even up to, say 800% of thestoichiometric amount. The regeneration efficiency depends to a greatdegree on such variables as column dimensions, conditions of operation,and purity required of the product. In plant-scale operations, fromabout 150 to 250% of the stoichiometric amount will be found sufficient.

Alternatively, the exhausted resin which is the H80 form can beregenerated without contacting it with an aqueous solution. For thispurpose, the resin is first converted to the OH form by treatment with abase such as KOH in alcoholic solution, and then the OH- form isconverted to the desired CO form by passing gaseous CO through thecolumn after the interstitial alcoholic solution has been drained. Aliberal excess of base even up to, say, 800% of the stoichiometricamount may be desirable to obtain complete conversion to the OH- form,but usually from about 150 to 200% of the stoichiometric amount will beeconomically more advantageous.

Sulfur dioxide can also be removed by anion ex- 1 changers of theabove-mentioned type in the S0 form.

The mechanism of S0 uptake then is exclusively reaction 2. The advantageof this method is that the column can be regenerated for renewed usesimply by washing with solvent, thus reverting reaction 2. However, thecapacity of the resin for S0 uptake when used in the S0 form is onlyhalf as high as when used in the C6 form.

The invention contemplates the use of strong base anionic exchangeresins, and, in fact, practically any strong base anionic exchange resinmay be employed. As a class, these resins are high molecular weight polybases which are virtually insoluble in the media wherein they are to beused. They consist of a 3-dimensional polymer network to which areattached a plurality of cationic radicals which maintain their cationiccharacter regardless of pH. These act as the anion exchangers.Especially suitable are the quaternary ammonium anion exchange resins,typical of which are the products of amination with the trimethyl amineor dimethyl ethanol amine of chloromethylated polymers, for example,chlorornethylated styrene-divinyl benzene copolymers. Representativecommercially available exchangers of these types are Amberlite IRA-400,lRA40l and IRA-410 of Rohm and Haas Company; Dowex-l and Dowex-Z of DowChemical Company, Nalcite SBR and SAR of National Aluminate Corporation,Permutit S2 of Permutit Cornpany and Duolite A42 and A4() of ChemicalProcess Company. US. Patents 2,388,235 and 2,591,573 describe processesfor producing ammonium exchange resins which can be converted to saltsuseful in practicing the invention. The Dowex and Nalcite resins are ofthe general formula R N+-A, in which one of the Rs is derived frompolystyrene which has been cross-linked with divinyl benzene. In thecase of Dowex 2 and Nalcite SAR, two

' R groups are methyl groups and one R group is a hydroxyforthhereinbefore. An exchanger in the form of the anion of an acid withionization constant (K,,) less than l0 is particularly desirable.

It has been found that the equilibrium of the reaction set forth inEquation 3 is driven virtually to completion on the resin. Moreover, thefront boundary of the SO; zone in the bed is thus self-sharpening. Ithas also been found that the break-through capacity of the resin isabout 1.11 moles of S0 per liter of resin bed. This is more than ofover-all ion exchange capacity of the resin. Moreover, it has been foundin the commercial preparation of sulfolane that with a feed containing450 ppm. S0 about 200 bed volumes can be processed in one cycle. Undersuch conditions the removal of S0 contaminant from the sulfolene is inexcess of 99.3%. The use of alcohol, such as isopropyl alcohol, does notadversely affect the resin life.

In accordance with the invention, when the ion exchange is conducted inthe absence of alcohol, such as isopropyl alcohol, the resin may then bein the base or hydroxy form. On the other hand, it is a preferredembodiment to use the ion exchanger in the presence of alcohol which mayor may not contain minor amounts of water, when the resin may then be inthe form of a salt such as, for example, the acetate or carboxylatesalt. The salt form of the resin is preferred in this latter instance tominimize loss of sulfolene by formation of ether with the alcohol whichis catalyzed by a resin in strong base form.

Example Conditioning of the Resin.A portion of Dowex 1-X8 standard gradeanion exchanger resin was conditioned by repeated anion exchange cyclesalternately with 1 M NaOl-l and l M HCl (about 4 liters per 50 grams ofresin per cycle for 4 hours), and washing with distilled water (about 4liters) after each conversion. Conditioning was carried out on a Euchnerfunnel in such a manner that the resin never became dry. The resinso-con ditioned was stored in C1 form under about 0.1% NaCl solution.

Preparation 07 the Column.-About 500 grams of the resin were convertedto CO form in a column of 2 inches in diameter by passing therethroughabout 8 liters of. l M aqueous Na CO solution. Tests for Clin the lastfractions of the effluent were negative. The resin was then washed with4 liters of methanol and subse quentiy with 8 liters of isopropylalcohol. 60 ml. of the resin were transferred into a column of 1 inchinternal diameter. The bed was backwashed with isopropyl alcohol.

Preparation of Feed.A feed containing 450 ppm. S0 and major amounts ofsulfolene was produced from the condensation reaction of butadiene withS0 in isopropyl alcohol, followed by stripping most of the untreated SOtherefrom.

Column Operari0n.-The feed was passed through the column at a flow rateof about 3 to 5' bed volumes per hour. Regular titration checks for theappearance of S0 in the eiiiuent were performed. 50 in the efiluent wasfirst detected when 200 bed volumes of feed had passed through thecolumn. The total efiiuent up to this point contained less than 3 ppm.50 the first 50 bed volumes less than 0.2 ppm.

Hydrogenation.The sulfolene thus freed from contaminating S0 was fedinto a hydrogenation zone wherein sulfolane was produced byhydrogenating in the presence of a Raney nickel catalyst. The life ofthis catalyst was prolonged indefinitely and substantially puresulfolane resulted therefrom.

Regeneration of Resin-An excess of Na CO was used as rcgenerant afterdraining the column. Such excess was several times the stoichiometricamount and the sodium carbonate solution was passed into the columnupwardly and withdrawn from the top thereof. The resin was then found tobe in renewed condition for further S0 removal.

With regard to the particular type of alcohol to be used in thecondensation reaction between the alkadiene and the sulfiur dioxide,isopropyl alcohol has proven particularly useful in that it reduces theformation of polysulfone and improves separation by filtration of anypolysulfone which may be formed.

The sulfolanes manufactured in this manner are particularly useful asselective solvents for the separation of organic compounds. They arespecifically applicable to the separation of mixtures of hydrocarbons ofdifferent degrees ofi saturation such as, for example, the separation ofaromatics from non-aromatics, olefins from diolefins and monoolefinsfrom saturates. The sulfolanes produced by this invention possess anenhanced stability in the processes involved in such extractions.

We claim as our invention:

1. In a process for the synthesis of a sulfolane which comprisesreacting a conjugated alkadiene with sulfur dioxide to form a reactionproduct containing essentially a corresponding sulfolene andcatalytically hydrogenating a sulfolene to a corresponding sulfolane inthe presence of asulfur-sensitive hydrogenation catalyst, theimprovement of treating the reaction product containing the sulfiolenewith a strong base anionic exchange resin consisting essentially of ahigh molecular weight polymeric network to which are attached aplurality of cationic radicals to substantially remove sulfur-containingpoisons of catalytic hydrogenation catalysts.

2. Process in accordance with claim 1 wherein the strong base anionicexchanger is in CO form.

3. Process in accordance with claim 1 wherein the anionic exchanger isin the form of the anion of an acid with K les than 10*.

4. Process in accordance with claim 1 wherein the strong base anionicexchanger is in SO form.

5. Process in accordance with claim 1 wherein the alkadiene isbutadiene.

6. Process in accordance with alltadiene is isoprene.

7. Process in accordance with claim 1 wherein the sulfolene contaminatedwtih sulfur dioxide is treated with a strong base anion exchanger in theform of a salt of a weak acid in the presence of a monohy-dric alcoholcontaining from one to four carbon atoms.

8. Process in accordance with claim 7 wherein said monohydric alcohol isisopropanol.

9. Process in accordance with claim 1 wherein the hydrogenating 015 thesulfolene is efiected prior to the reversion of substantial amounts ofthe sulfolene.

claim 1 wherein the References Cited in the file of this patent UNITEDSTATES PATENTS 2,360,859 Evans et al. Oct. 24, 1944 2,451,298 Morris etal. Oct. 12, 1948 2,578,565 Mahan et a1. Dec. 11, 1951 FOREIGN PATENTS936,442 Germany Dec. 15, 1955 OTHER REFERENCES Calman et al.: IonExchangers in Organic and Biochemistry, 1957, Interscience Publishers,Inc., New York, New York, page 642, i

1. IN A PROCESS FOR THE SNTHESIS OF A SULFOLANE WHICH COMPRISES REACTINGA CONJUGATED ALKADIENE WITH SULFUR DIOXIDE TO FORM A REACTION PRODUCTCONTAINING ESSENTIALLY A CORRESPONDING SULFOLENE AND CATALYTICALLYHYDROGENATING A SULFONENE TO A CORRESPONDING SLFOLANE IN THE PRESENCE OFASULFUR-SENSITIVE HYDROGENATION CATALYST, THE IMPROVEMENT OF TREATINGTHE REACTION PRODUCT CONTAINING THE SULFOLENE WITH A STRONG BASE ANIONICEXCHANGE RESIN CONSISTING ESSENTIALLY OF A HIGH MOLECULAR WEIGHTPOLYMERIC NETWORK TO WHICH ARE ATTACHED A PLURALITY OF CATIONIC RADICALSTO SUBSTANTIALLY REMOVE SULFUR-CONTAINING POISONS OF CATALYTICHYDROGENATION CATALYSTS.